1. Field of the Invention
This invention relates to solar cell structures and other light sensing devices and fabrication techniques, and more particularly to compact, low weight high voltage light sensitive devices and a related fabrication method that is compatible with a wide range of cell materials.
2. Description of the Related Art
It is generally desirable to use monolithic fabrication techniques in forming solar cell arrays, in which a basic cell is replicated over a unitary structure. Monolithic fabrication provides a low cost, high volume manufacturing capability, and a high quality array. Such an array is shown in U.S. Pat. No. 4,278,473 to Borden. The Borden patent describes solar cell arrays, in this case monolithic, of which the individual cells are formed on a common semi-insulating substrate and interconnected with each other. In the Borden patent, a pair of epitaxial layers are formed on the common substrate to provide the active cell material. Breaks are made in the two epitaxial layers to electrically isolate the cells from each other, with the semi-insulating substrate continuing to provide a common carrier for all of the cells. To connect adjacent cells in series, electrical leads are connected from the upper surface of one cell to a contact ledge on the side of the base epitaxial region for an adjacent cell, following the contours of the break between the two cells.
Although a monolithic fabrication process such as that used in the Borden patent is a definite improvement over discrete fabrication, to date the required semi-insulating substrates are available only for gallium arsenide. Silicon and germanium are common solar cell materials that are less expensive than gallium arsenide, but they have not been found to be compatible with monolithic fabrication techniques. Even with monolithic gallium arsenide construction, it would desirable to further reduce the cost and bulk of the resulting photovoltaic arrays.